DiSTeM, Università di Palermo, Italy

Volcanoes emit SO2, CO2, andH2S, but also trace elements gases and particles such as As, Cd, Cr, Cu, Hg, Ni, Pb, and Sb. Active moss bag biomonitoring, an easy to apply and low budget method, was used to determine trace element release from volcanic areas of different geological context and climates. Exposure height variations (0.7–1.6 m above ground) due to different availability of natural tie points did not affect the results. Accumulation was linear for exposure durations from three days to nine weeks, so values were comparable by normalization to moss exposure time. Uncovered moss bags showed higher accumulation than co-exposed covered ones because of additional dust and wet deposition while washout by rain was negligible. The selection of a specific moss significantly affected element accumulation with moss of lower shoot compactness accumulating more. For all volcanic areas, highest accumulation was found for S (1–1000 μmol·(g·d)−1), followed by Fe and Mg (0.1–10 μmol·(g·d)−1), Sr, Ba, Pb, Cr, Li (10−4–10−1 μmol·(g·d)−1), then Co, Mo and the volatile elements As, Sb, Se, Tl, Bi (10−6–10−2 μmol·(g·d)−1). Formost elements, open conduit volcanoes (Etna, Stromboli, Nyiragongo) showed highermoss accumulation rates than more quiescent hydrothermal areas (Vulcano > Nisyros > Yellowstone National Park) and a correlation of S, Fe, and Pb fromeruptive ash and lava emissions. For some volatile elements (S, As, Se), higher accumulation was observed within fumarolic fields compared to crater rims of open conduit volcanoes which is a relevant information for risk assessment of tourist exposure to volcanic gases.

The composition and fluxes of volcanic gases released by persistent open-vent degassing at Bromo Volcano, east Java (Indonesia), were characterised in September 2014 from both in-situ Multi-GAS analysis and remote spectroscopic (dual UVcamera)measurements of volcanic plumeemissions. Our results demonstrate that Bromo volcanic gas is water-rich (H2O/SO2 ratios of 56–160) and has CO2/SO2 (4.1 ± 0.7) and CO2/Stot (3.2 ± 0.7) ratios within the compositional range of other high-temperature magma-derived gases in Indonesia. H2/H2O and H2S/SO2 ratios constrain a magmatic gas source with minimal temperature of ~700 °C and oxygen fugacity of 10-17–10-18 bars. UV camera sensing on September 20 and 21, 2014 indicates a steady daily mean SO2 output of 166 ± 38 t d−1, which is ten times higher than reported from few previous studies. Our results indicate that Bromo ranks amongst the strongest sources of quiescent volcanic SO2 emission measured to date in Indonesia, being comparable to Merapi volcano in central Java. By combining our results for the gas composition with the SO2 plume flux, we assess for the first time the fluxes of H2O (4725 ± 2292 t d−1), CO2 (466 ± 83 t d−1), H2S (25 ± 12 t d−1) and H2 (1.1 ± 0.8) from Bromo. Our study thus contributes a new piece of information to the still limited data base for volcanic gas emissions in Indonesia, and confirms that much remain to be done to fully assess the contribution of this very active arc region to global volcanic gas fluxes.